Are there any cosplay events you plan on attending?
The way most people go about forming cosplay groups is to ask if anyone else is cosplaying from the same series at the same specific event and then agreeing on the best day and time for a meet-up. If you're not familiar with what will be running there is a list of events that you can find at the top of the page. If you're new to cosplay then I'd suggest seeing if you can pop along to one of the MCM Expos ^^